(a) The Field of the Invention
The present invention relates to low viscosity unsaturated polyester resins, essentially comprising an unsaturated polyester alkyd and an ethylenically unsaturated monomer copolymerizable with the alkyd. The present invention further relates to products, optionally reinforced with glass fibers, obtained from said polyester resins by the conventional unsaturated polyester processing techniques.
(b) The Prior Art
Commercial products called "unsaturated polyester resins", obtained by mixing an unsaturated polyester alkyd with a copolymerizable monomer, are known; the known polyester resins however have a higher viscosity than the resins of the present invention, the monomer content and the elastic moduls and heat distortion temperature (HDT) of the hardened pure resin being equal. In other words, the applicant has surprisingly found, and this forms an object of the present invention, that it is possible to obtain low viscosity unsaturated polyester resins with low styrene content, adapted for making products by the conventional unsaturated polyester resin processing techniques.